1. Field of the Invention
The present invention relates to a semiconductor quantum well laser manufactured by use of methods such as a molecular beam epitaxial method.
2. Description of the Prior Art.
As a semiconductor quantum well laser manufactured with a barrier layer having a thickness of at most 1000 .ANG., there has been one described in pages 371 to 373 of "LOW-THRESHOLD, HIGH-POWER ZERO-ORDER LATERAL-MODE DQW-SCH METAL-CLAD RIDGE WAVEGUIDE (AlGa)As/GaAs LASERS" written by B. Garrett et al and published in ELECTRONICS LETTERS, 9th Apr. 1987, Vol. 23, No. 8. This is of a Separately Confined Heterostructure (SCH) and there is formed a quantum well enclosed with barrier layers each of Al.sub.0.2 GA.sub.0.8 As with a thickness of at most 1000 .ANG..
However, in the semiconductor quantum well laser above, the component ratio of Al is 0.4 in the clad layer and 0.2 in the barrier layer, namely, there exist two kinds of Al component ratios, which hence requires to employ two Al cells for manufacturing the laser.
In addition, when it is desired to emit a light having a short wavelength, since there is used a mixed crystal barrier layer of AlGaAs, the X point (indirect transition) becomes to be located at a position near the .GAMMA. point (direct transition) in the barrier layer (for example, when it is desired to obtain an emission of light with a wavelength of about 680 nm, the Al component ratio becomes to be 0.4 to 0.5 and hence the distance between the X point and the .GAMMA. point is descreased). In consequence, the transition from the X point is further facilitated, and this does not contribute to the light emission, which leads to problems that the leakage of the injection carriers is increased and that the threshold current becomes greater and the temperature characteristic is deteriorated.